As consumers are demanding higher bandwidth communication channels, the fibre optic communication networks of telecommunications companies are reaching closer to the end users. The extending of optical communication networks closer to the user such that the optical network replaces the more traditional copper local loop, is known as fibre to the X (FTTx). The optical fibre network may extend to a cabinet that serves a neighbourhood. Alternatively it may extend to the kerbside to serve several customers. The optical fibre based network may also extend as far as the building or to the end user's home or business. These types of optical network architectures can be realised using a Passive Optical Network.
A passive optical network has a point to multipoint architecture in which optical splitters are used such that a single optical fibre serves multiple end users. A passive optical network comprises an Optical Line Termination node (OLT) contained in the telephone exchange or central office or street side cabinet, for example, at least one optical splitter and an Optical Network Termination (ONT) at the end user's premises. Optical fibres are used to connect the optical line termination node to the optical network termination nodes. Thus, downstream signals are broadcast to all of the optical network termination nodes that are connected to the optical line termination node via the passive optical network. Upstream signals are typically based on Time Division Multiple Access communication scheme (TDMA). Thus, the end user needs to timeshare the optical medium given that only one end user can transmit at any given time. A passive optical network configuration is advantageous as it is cost effective as a minimum amount of network equipment is required to serve several end users.
However, as upstream communication on the passive optical network is timeshared using TDMA, if one optical network termination node does not obey its allocated transmission time slot, and sends continuous or unsynchronised light (ie outside its allocated time slot assigned by the optical line termination node scheduling function), this will seriously impair, or make impossible, the upstream communication for the other optical network termination nodes of the passive optical network. This scenario, with a malicious end user is sometimes referred to as a “rogue ONT”. The rogue optical network termination node can operate in several ways to disrupt communication over the passive optical network.
The rogue ONT may have a continuous light source connected to the fibre optic connector that normally connects the optical network termination node to the passive optical network. This can then be used to disrupt communication for the other optical network termination nodes. Alternatively, the rogue ONT may have its software or hardware manipulated to make it emit light continuously or emit unsynchronised light.